Monday, November 30, 2009

Black Squirrel & Melanism

Nature Watch
By Susan Benson,
CNHM Director of Education

This week I was driving towards Winter School District to teach science and environmental education for the day, and thought to myself, “What is happening this week in the natural world that I should write about?” Not even thirty seconds later, a black squirrel ran across the road in front of me. I smiled as nature so quickly gave me an answer. What is it that causes these animal colorations?

The official word for this animal coloration is melanism. The black squirrels we see on occasion are really eastern gray squirrels with a genetic mutation. Melanism is an increased amount of black or nearly black pigmentation of skin, feathers or hair. Dark or even black squirrels or deer are said to be melanistic. These animals have too much pigment in their eyes, hair and skin, rather than too little. Biologists estimate that about one of every ten thousand squirrels has black coloration. Melanistic black squirrels can exist wherever gray squirrels live. Gray mating pairs may produce black offspring, and in areas with high concentrations of black squirrels, mixed litters can be found.

This black color phase in squirrels is not believed to be a genetic mistake, however. Before European settlers, it is reported that almost all squirrels in the northern states were black. Black fur absorbs more heat from the sun in our cold northern winters, and the coloration can be a defense in shaded, denser and dark forests. This darker color could have aided in hiding from predators of the sky. One scientist in particular, Dr. Bill Hamilton, suggests that as Europeans settled in this region, forests were cleared, farmland became a common use, and squirrels were hunted extensively as a food source and a perceived threat to farm crops. As this forest became more broken up, the black color was more easily seen, and so began to disappear from the population.

Black squirrels have gained great notoriety throughout the United States. Black squirrels have been introduced into one city to outcompete red squirrels. Some communities had black squirrels gifted to them, while another town has a legend that their populations came from a traveling circus. Some U.S. towns and one in Canada publicize with pride their black squirrel population. At least five colleges use the black squirrel as a symbol or mascot. Local residents in the Chicago area participated in a message board to share their own observations and “scientific” studies on the activities of their local black squirrel populations. Finally, in some alternative weather forecasting, black squirrel sightings are used to predict that devastatingly harsh winters are ahead. Let us hope that my sighting is not evidence that this type of winter is headed our way! In the mean time, enjoy looking for your own black squirrel nearby.

For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility and exhibits, the Curiosity Center and Brain Teasers 2, in Cable at 13470 County Highway M. Also find us on the web at to learn more about exhibits and programs.

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